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1.
The feasibility of biologically removing nitrate from groundwater was tested by using cyanobacterial cultures in batch mode under laboratory conditions. Results demonstrated that nitrate-contaminated groundwater, when supplemented with phosphate and some trace elements, can be used as growth medium supporting vigorous growth of several strains of cyanobacteria. As cyanobacteria grew, nitrate was removed from the water. Of three species tested, Synechococcus sp. strain PCC 7942 displayed the highest nitrate uptake rate, but all species showed rapid removal of nitrate from groundwater. The nitrate uptake rate increased proportionally with increasing light intensity up to 100 μmol of photons m −2 s −1, which parallels photosynthetic activity. The nitrate uptake rate was affected by inoculum size (i.e., cell density), fixed-nitrogen level in the cells in the inoculum, and aeration rate, with vigorously aerated, nitrate-sufficient cells in mid-logarithmic phase having the highest long-term nitrate uptake rate. Average nitrate uptake rates up to 0.05 mM NO 3− h −1 could be achieved at a culture optical density at 730 nm of 0.5 to 1.0 over a 2-day culture period. This result compares favorably with those reported for nitrate removal by other cyanobacteria and algae, and therefore effective nitrate removal from groundwater using this organism could be anticipated on large-scale operations. 相似文献
2.
Aerobic and anaerobic groundwater continuous-flow microcosms were designed to study nitrate reduction by the indigenous bacteria in intact saturated soil cores from a sandy aquifer with a concentration of 3.8 mg of NO 3−-N liter −1. Traces of 15NO 3− were added to filter-sterilized groundwater by using a Darcy flux of 4 cm day −1. Both assimilatory and dissimilatory reduction rates were estimated from analyses of 15N 2, 15N 2O, 15NH 4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N 2 and N 2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO 3− and NH 4+ were analyzed as pentafluorobenzoyl amides by multiple-ion monitoring and protein amino acids as their N-heptafluorobutyryl isobutyl ester derivatives by negative ion-chemical ionization. The numbers of bacteria and their [ methyl- 3H]thymidine incorporation rates were simultaneously measured. Nitrate was completely reduced in the microcosms at a rate of about 250 ng g −1 day −1. Of this nitrate, 80 to 90% was converted by aerobic denitrification to N 2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO 3− was reduced to NH 4+. Assimilatory reduction was recorded only in the aerobic microcosm, where N appeared in alanine in the cells. The nitrate reduction rates estimated for the aquifer material were low in comparison with rates in eutrophic lakes and coastal sediments but sufficiently high to remove nitrate from an uncontaminated aquifer of the kind examined in less than 1 month. 相似文献
3.
Coastal zones act as a sink for riverine and atmospheric nitrogen inputs and thereby buffer the open ocean from the effects of anthropogenic activity. Recently, microbial activity in sandy permeable sediments has been identified as a dominant source of N-loss in coastal zones, namely through denitrification. Some of the highest coastal denitrification rates measured so far occur within the intertidal permeable sediments of the eutrophied Wadden Sea. Still, denitrification alone can often account for only half of the substantial nitrate (NO 3
−) consumption. Therefore, to investigate alternative NO 3
− sinks such as dissimilatory nitrate reduction to ammonium (DNRA), intracellular nitrate storage by eukaryotes and isotope equilibration effects we carried out 15NO 3
− amendment experiments. By considering all of these sinks in combination, we could quantify the fate of the 15NO 3
− added to the sediment. Denitrification was the dominant nitrate sink (50–75%), while DNRA, which recycles N to the environment accounted for 10–20% of NO 3
− consumption. Intriguingly, we also observed that between 20 and 40% of 15NO 3
− added to the incubations entered an intracellular pool of NO 3
− and was subsequently respired when nitrate became limiting. Eukaryotes were responsible for a large proportion of intracellular nitrate storage, and it could be shown through inhibition experiments that at least a third of the stored nitrate was subsequently also respired by eukaryotes. The environmental significance of the intracellular nitrate pool was confirmed by in situ measurements which revealed that intracellular storage can accumulate nitrate at concentrations six fold higher than the surrounding porewater. This intracellular pool is so far not considered when modeling N-loss from intertidal permeable sediments; however it can act as a reservoir for nitrate during low tide. Consequently, nitrate respiration supported by intracellular nitrate storage can add an additional 20% to previous nitrate reduction estimates in intertidal sediments, further increasing their contribution to N-loss. 相似文献
4.
NO 3− concentration profiles were measured in the sediments of a meso-eutrophic lake with a newly developed microelectrode. The depth of penetration of NO 3− varied from only 1.3 mm in organic-rich profundal silty sediments to 5 mm in organic-poor littoral sandy sediments. The thickness of the zone of denitrification in the organic-rich sediments was <500 μm. Oxygen profiles measured simultaneously revealed that the zone of denitrification was directly adjacent to the aerobic zone. The results demonstrate high denitrification rates (0.26 to 1.31 mmol m −2 day −1) at in situ nitrate concentrations in the overlying water (0.030 mmol liter −1) and limitation of denitrification by nitrate availability. 相似文献
5.
The kinetics of several steps in the microbial denitrification process in Brookston clay and Fox sandy loam, two soils common to Southwestern Ontario, were studied in the temperature range of 5 to 25°C. The extent of chemical denitrification was also determined in otherwise identical but sterilized soils at temperatures up to 80°C. A gas flow system was used in which soil gases were continuously removed from anaerobic soil columns by argon carrier gas. Net steady-state rates of NO and N 2O production, rates of loss of NO 3−, and production and loss of NO 2− were measured over periods of up to 5 days. Arrhenius activation energies for the zero-order process NO 3− → NO 2− were calculated to be 50 ± 9 kJ mol −1 for Brookston clay and 55 ± 13 kJ mol −1 for Fox sandy loam. The overall reaction, NO 2− → NO (chemodenitrification), in both sterile soils was accurately first order with respect to NO 2−; the activation energy was 70 ± 2.8 kJ mol −1 in Brookston clay and 79 ± 1.2 kJ mol −1 in the sandy loam, and the preexponential factors were (2.3 ± 1.2) × 10 9 and (5.7 ± 1.2) × 10 9 min −1, respectively. 相似文献
6.
Nitrate reductase activity in excised embryos of Agrostemma githago increases in response to both NO 3− and cytokinins. We asked the question whether cytokinins affected nitrate reductase activity directly or through NO 3−, either by amplifying the effect of low endogenous NO 3− levels, or by making NO 3− available for induction from a metabolically inactive compartment. Nitrate reductase activity was enhanced on the average by 50% after 1 hour of benzyladenine treatment. In some experiments, the cytokinin response was detectable as early as 30 minutes after addition of benzyladenine. Nitrate reductase activity increased linearly for 4 hours and began to decay 13 hours after start of the hormone treatment. When embryos were incubated in solutions containing mixtures of NO 3− and benzyladenine, additive responses were obtained. The effects of NO 3− and benzyladenine were counteracted by abscisic acid. The increase in nitrate reductase activity was inhibited at lower abscisic acid concentrations in embryos which were induced with NO 3−, as compared to embryos treated with benzyladenine. Casein hydrolysate inhibited the development of nitrate reductase activity. The response to NO 3− was more susceptible to inhibition by casein hydrolysate than the response to the hormone. When NO 3− and benzyladenine were withdrawn from the medium after maximal enhancement of nitrate reductase activity, the level of the enzyme decreased rapidly. Nitrate reductase activity increasd again as a result of a second treatment with benzyladenine but not with NO 3−. At the time of the second exposure to benzyladenine, no NO 3− was detectable in extracts of Agrostemma embryos. This is taken as evidence that cytokinins enhance nitrate reductase activity directly and not through induction by NO 3−. 相似文献
7.
Chlamydomonas reinhardii cells, growing photoautotrophically under air, excreted to the culture medium much higher amounts of NO 2− and NH 4+ under blue than under red light. Under similar conditions, but with NO 2− as the only nitrogen source, the cells consumed NO 2− and excreted NH 4+ at similar rates under blue and red light. In the presence of NO 3− and air with 2% CO 2 (v/v), no excretion of NO 2− and NH 4+ occurred and, moreover, if the bubbling air of the cells that were currently excreting NO 2− and NH 4+ was enriched with 2% CO 2 (v/v), the previously excreted reduced nitrogen ions were rapidly reassimilated. The levels of total nitrate reductase and active nitrate reductase increased several times in the blue-light-irradiated cells growing on NO 3− under air. When tungstate replaced molybdate in the medium (conditions that do not allow the formation of functional nitrate reductase), blue light activated most of the preformed inactive enzyme of the cells. Furthermore, nitrate reductase extracted from the cells in its inactive form was readily activated in vitro by blue light. It appears that under high irradiance (90 w m −2) and low CO 2 tensions, cells growing on NO 3− or NO 2− may not have sufficient carbon skeletons to incorporate all the photogenerated NH 4+. Because these cells should have high levels of reducing power, they might use NO 3− or, in its absence, NO 2− as terminal electron acceptors. The excretion of the products of NO 2− and NH 4+ to the medium may provide a mechanism to control reductant level in the cells. Blue light is suggested as an important regulatory factor of this photorespiratory consumption of NO 3− and possibly of the whole nitrogen metabolism in green algae. 相似文献
8.
Soybean ( Glycine max [L.] Merr.) seeds were imbibed and germinated with or without NO 3−, tungstate, and norflurazon (San 9789). Norflurazon is a herbicide which causes photobleaching of chlorophyll by inhibiting carotenoid synthesis and which impairs normal chloroplast development. After 3 days in the dark, seedlings were placed in white light to induce extractable nitrate reductase activity. The induction of maximal nitrate reductase activity in greening cotyledons did not require NO 3− and was not inhibited by tungstate. Induction of nitrate reductase activity in norflurazon-treated cotyledons had an absolute requirement for NO 3− and was completely inhibited by tungstate. Nitrate was not detected in seeds or seedlings which had not been treated with NO 3−. The optimum pH for cotyledon nitrate reductase activity from norflurazon-treated seedlings was at pH 7.5, and near that for root nitrate reductase activity, whereas the optimum pH for nitrate reductase activity from greening cotyledons was pH 6.5. Induction of root nitrate reductase activity was also inhibited by tungstate and was dependent on the presence of NO 3−, further indicating that the isoform of nitrate reductase induced in norflurazon-treated cotyledons is the same or similar to that found in roots. Nitrate reductases with and without a NO 3− requirement for light induction appear to be present in developing leaves. In vivo kinetics (light induction and dark decay rates) and in vitro kinetics (Arrhenius energies of activation and NADH:NADPH specificities) of nitrate reductases with and without a NO 3− requirement for induction were quite different. Km values for NO 3− were identical for both nitrate reductases. 相似文献
9.
The effect of nitrogen form (NH 4-N, NH 4-N + NO 3−, NO 3−) on nitrate reductase activity in roots and shoots of maize ( Zea mays L. cv INRA 508) seedlings was studied. Nitrate reductase activity in leaves was consistent with the well known fact that NO 3− increases, and NH 4+ and amide-N decrease, nitrate reductase activity. Nitrate reductase activity in the roots, however, could not be explained by the root content of NO 3−, NH 4-N, and amide-N. In roots, nitrate reductase activity in vitro was correlated with the rate of nitrate reduction in vivo. Inasmuch as nitrate reduction results in the production of OH − and stimulates the synthesis of organic anions, it was postulated that nitrate reductase activity of roots is stimulated by the released OH − or by the synthesized organic anions rather than by nitrate itself. Addition of HCO 3− to nutrient solution of maize seedlings resulted in a significant increase of the nitrate reductase activity in the roots. As HCO 3−, like OH −, increases pH and promotes the synthesis of organic anions, this provides circumstantial evidence that alkaline conditions and/or organic anions have a more direct impact on nitrate reductase activity than do NO 3−, NH 4-N, and amide-N. 相似文献
10.
We examined nitrate assimilation and root gas fluxes in a wild-type barley ( Hordeum vulgare L. cv Steptoe), a mutant ( nar1a) deficient in NADH nitrate reductase, and a mutant ( nar1a; nar7w) deficient in both NADH and NAD(P)H nitrate reductases. Estimates of in vivo nitrate assimilation from excised roots and whole plants indicated that the nar1a mutation influences assimilation only in the shoot and that exposure to NO 3− induced shoot nitrate reduction more slowly than root nitrate reduction in all three genotypes. When plants that had been deprived of nitrogen for several days were exposed to ammonium, root carbon dioxide evolution and oxygen consumption increased markedly, but respiratory quotient—the ratio of carbon dioxide evolved to oxygen consumed—did not change. A shift from ammonium to nitrate nutrition stimulated root carbon dioxide evolution slightly and inhibited oxygen consumption in the wild type and nar1a mutant, but had negligible effects on root gas fluxes in the nar1a; nar7w mutant. These results indicate that, under NH 4+ nutrition, 14% of root carbon catabolism is coupled to NH 4+ absorption and assimilation and that, under NO 3− nutrition, 5% of root carbon catabolism is coupled to NO 3− absorption, 15% to NO 3− assimilation, and 3% to NH 4+ assimilation. The additional energy requirements of NO 3− assimilation appear to diminish root mitochondrial electron transport. Thus, the energy requirements of NH 4+ and NO 3− absorption and assimilation constitute a significant portion of root respiration. 相似文献
11.
The effect of water stress on patterns of nitrate reductase activity in the leaves and nodules and on nitrogen fixation were investigated in Medicago sativa L. plants watered 1 week before drought with or without NO 3−. Nitrogen fixation was decreased by water stress and also inhibited strongly by the presence of NO 3−. During drought, leaf nitrate reductase activity (NRA) decreased significantly particularly in plants watered with NO 3−, while with rewatering, leaf NRA recovery was quite important especially in the NO 3−-watered plants. As water stress progressed, the nodular NRA increased both in plants watered with NO 3− and in those without NO 3− contrary to the behavior of the leaves. Beyond −15.10 5 pascal, nodular NRA began to decrease in plants watered with NO 3−. This phenomenon was not observed in nodules of plants given water only. 相似文献
12.
Effects of NO 2−, ClO 3−, and ClO 2− on the induction of nitrate transport and nitrate reductase activity (NRA) as well as their effects on NO 3− influx into roots of intact barley ( Hordeum vulgare cv Klondike) seedlings were investigated. A 24-h pretreatment with 0.1 mol m −3 NO 2− fully induced NO 3− transport but failed to induce NRA. Similar pretreatments with ClO 3− and ClO 2− induced neither NO 3− transport nor NRA. Net ClO 3− uptake was induced by NO 3− but not by ClO 3− itself, indicating that NO 3− and ClO 3− transport occur via the NO 3− carrier. At the uptake step, NO 2− and ClO 2− strongly inhibited NO 3− influx; the former exhibited classical competitive kinetics, whereas the latter exhibited complex mixed-type kinetics. ClO 3− proved to be a weak inhibitor of NO 3− influx ( Ki = 16 mol m −3) in a noncompetitive manner. The implications of these findings are discussed in the context of the suitability of these NO 3− analogs as screening agents for the isolation of mutants defective in NO 3− transport. 相似文献
13.
The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland. The available inorganic nitrogen in the adjacent coastal waters decreases from 50–80 μmol NO 3 -/l and 6–15 μmol NH 4 +/l in early spring to ca one tenth during the growing season. In the sediment of the tidal flats available ammonia and nitrate vary between 50 and 100 μmol/1 pw. In the salt marsh available ammonia increases from 200–300 nmol NH 4 +/g fwt to approximately double the amount, and the available nitrate varies from 100–300 nmol NO 3 -/g fwt (250–750 μmol NO 3 -/l pw) to ca one third during the growing season. The exchange of NH 4 +, NO 2 - and NO 3 - across the sediment water interface has been estimated during tidal cycles under light and dark conditions on the tidal flats. The flux of nitrogen was dependent on the flora and fauna as well as the time of the year. The tidal activity, frequency and length of inundation are considered the driving force in a two-way process between salt marshes and adjacent coastal waters. The role of marsh sediment, tidal water and sediments of the tidal flats as sites of accumulation, consumption and remineralization of organic matter is emphasized. The possible exchange of ammonia and nitrate between the salt marsh and the different compartments of the tidal water is discussed. 相似文献
14.
The influence of nitrogen stress on net nitrate uptake resulting from concomitant 15NO 3− influx and 14NO 3− efflux was examined in two 12-day-old inbred lines of maize. Plants grown on 14NO 3− were deprived of nitrogen for up to 72 hours prior to the 12th day and then exposed for 0.5 hour to 0.15 millimolar nitrate containing 98.7 atom% 15N. The nitrate concentration of the roots declined from approximately 100 to 5 micromolar per gram fresh weight during deprivation, and 14NO 3− efflux was linearly related to root nitrate concentration. Influx of 15NO 3− was suppressed in nitrogen-replete plants and increased with nitrogen deprivation up to 24 hours, indicating a dissipation of factors suppressing influx. Longer periods of nitrogen-deprivation resulted in a decline in 15NO 3− influx from its maximal rate. The two inbreds differed significantly in the onset and extent of this decline, although their patterns during initial release from influx suppression were similar. Except for plants of high endogenous nitrogen status, net nitrate uptake was largely attributable to influx, and genetic variation in the regulation of this process is implied. 相似文献
15.
The objective of this study was to identify factors which limit leaf nitrate reductase (NR) activity as decline occurs during flowering and beginning seed development in soybean ( Glycine max [L.] Merr. cv Clark). Level of NR enzyme activity, level of reductant, and availability of NO 3− as substrate were evaluated for field-grown soybean from flowering through leaf senescence. Timing of reproductive development was altered within one genotype by (a) exposure of Clark to an artificially short photoperiod to hasten flowering and podfill, and (b) the use of an early flowering isoline. Nitrogen (N) was soil-applied to selected plots at 500 kilograms per hectare as an additional variable. Stem NO 3− concentration and in vivo leaf NR activity were significantly correlated ( R2 = 0.69 with nitrate in the assay medium and 0.74 without nitrate in the medium at P = 0.001) across six combinations of reproductive and soil N-treatment. The supply of NO 3− from the root to the leaf tissue was the primary limitation to leaf NR activity during flowering and podfill. Levels of NR enzyme and reductant were not limiting to leaf NR activity during this period. 相似文献
16.
Six genotypes of winter wheat ( Triticum aestivum L.) differing in grain protein concentration were grown on a nutrient solution containing low concentrations of NO 3− (2 millimolar). Total NO 3− uptake varied between genotypes but was not related to grain protein content. An in vivo nitrate reductase assay was used to determine the affinity of the enzyme for NO 3−, and large phenotypic variations were observed. In vivo estimations of the concentration and size of the metabolic pool were variable. However, the three genotypes with the higher ratios of metabolic pool size to leaf total NO 3− concentration were the high protein varieties. It is proposed that a high affinity of nitrate reductase for nitrate might be a biochemical marker for the capacity of the plant to continue assimilating NO 3− for a longer period during the last stage of growth. 相似文献
17.
The effect of NaCl and Na 2SO 4 salinity on NO 3− assimilation in young barley ( Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO 3− transporter was affected very little; the major effect of the salts was on its activity. Both Cl − and SO 42− salts severely inhibited uptake of NO 3−. When compared on the basis of osmolality of the uptake solutions, Cl − salts were more inhibitory (15-30%) than SO 42− salts. At equal concentrations, SO 42− salts inhibited NO 3− uptake 30 to 40% more than did Cl − salts. The absolute concentrations of each ion seemed more important as inhibitors of NO 3− uptake than did the osmolality of the uptake solutions. Both K + and Na + salts inhibited NO 3− uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity. Unlike NO3− uptake, NO3− reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO3− in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the `anaerobic' in vivo assay, was always greater than the actual in situ rate of NO3− reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO3− transporter, rather than that of the NO3− reduction system, may be a critical factor to plant survival during salt stress. 相似文献
18.
In vivo NO 3− reduction in roots and shoots of intact barley ( Hordeum vulgare L. var Numar) seedlings was estimated in light and darkness. Seedlings were placed in darkness for 24 hours to make them carbohydrate-deficient. During darkness, the leaves lost 75% of their soluble carbohydrates, whereas the roots lost only 15%. Detached leaves from these plants reduced only 7% of the NO 3− absorbed in darkness. By contrast, detached roots from the seedlings reduced the same proportion of absorbed NO 3−, as did roots from normal light-grown plants. The rate of NO 3− reduction in the roots accounted for that found in the intact dark-treated carbohydrate-deficient seedlings. The rates of NO 3− reduction in roots of intact plants were the same for approximately 12 hours, both in light and darkness, after which the NO 3− reduction rate in roots of plants placed in darkness slowly declined. In the dark, approximately 40% of the NO 3− reduction occurred in the roots, whereas in light only 20% of the total NO 3− reduction occurred in roots. A lesser proportion was reduced in roots because the leaves reduced more nitrate in light than in darkness. 相似文献
19.
The cytoplasmic NO 3− concentration ([NO 3−] c) was estimated for roots of barley ( Hordeum vulgare L. cv Klondike) using a technique based on measurement of in vivo nitrate reductase activity. At zero external NO 3− concentration ([NO 3−] o), [NO 3−] c was estimated to be 0.66 m m for plants previously grown in 100 μ m NO 3−. It increased linearly with [NO 3−] o between 2 and 20 m m, up to 3.9 m m at 20 m m [NO 3−] o. The values obtained are much lower than previous estimates from compartmental analysis of barley roots. These observations support the suggestion (MY Siddiqi, ADM Glass, TJ Ruth [1991] J Exp Bot 42: 1455-1463) that the nitrate reductase-based technique and compartmental analysis determine [NO 3−] c for two separate pools; an active, nitrate reductase-containing pool (possibly located in the epidermal cells) and a larger, slowly metabolized storage pool (possibly in the cortical cells), respectively. Given the values obtained for [NO 3−] c and cell membrane potentials of −200 to −300 mV (ADM Glass, JE Schaff, LV Kochian [1992] Plant Physiol 99: 456-463), it is very unlikely that passive influx of NO 3− is possible via the high-concentration, low-affinity transport system for NO 3−. This conclusion is consistent with the suggestion by Glass et al. that this system is thermodynamically active and capable of transporting NO 3− against its electrochemical potential gradient. 相似文献
20.
A computer-controlled multichannel data acquisition system was employed to obtain continuous measurements of net nitrate or chlorate uptake by roots of intact barley plants ( Hordeum vulgare cv Betzes) using nitrate-specific electrodes. Plants, previously grown in solutions maintained at 10 or 200 micromolar NO 3− (low N or high N conditions, respectively), were provided with 200 micromolar NO 3− or ClO 3− during the uptake period. Initial rates of NO 3− uptake were several times higher in low N plants than in high N plants. Within 10 min, uptake in the former plants declined to a new steady rate which was sustained for the remainder of the experiment. No such time-dependent changes were evident in the high N plants. Rates and patterns of net chlorate uptake exhibited almost identical dependence upon previous nitrate provision. NO 3− ( 36ClO 3−) influx, by contrast, appeared to be independent of NO 3− pretreatment prior to influx determination. Nitrate efflux, estimated by several different methods, was strongly correlated with internal nitrate concentration of the roots. 相似文献
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